I'm trying to create a desert planet, and I plan on having water be produced by slug-like beings that consume oxygen and hydrogen from the atmosphere and produce water as a by-product f their digestive system and was wondering if something like this would be plausible if it were to exists and around how much oxygen/hydrogen would need to exist for these creatures (around 3 KG in weight) would to produce around 2 liters of water every day (24 hours on earth). (so that a human could easily survive off of its water assuming they had food)

  • $\begingroup$ ???? Hydrogen is always happy to burn in oxygen producing water. If you have free hydrogen and free oxygen in the atmosphere then you need no fancy magical slugs; the two gases love each other very very much and are always ready and willing to combine at a moment's notice. (This is one of the reasons why there is just about no hydrogen in the atmosphere... If there was any it would quickly burn and become water.) $\endgroup$
    – AlexP
    Sep 26, 2022 at 22:31
  • $\begingroup$ yes but the slugs add to the planets life, as its very limited currently with only a few plant species and scarab-like insects/beetles and i als enjoy slugs $\endgroup$ Sep 26, 2022 at 22:33
  • $\begingroup$ Yes, I get it, but the problem is that you cannot have free oxygen and free hydrogen coexisting. They will combine given the slightest chance. $\endgroup$
    – AlexP
    Sep 26, 2022 at 22:34
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    $\begingroup$ We help people create imaginary worlds. When you ask if it's plausible, what do you mean? In the Real World? Of course it isn't. Do you mean does it meet the requirements of suspension of disbelief? Of course it would! all you need is a way for it to acquire free hydrogen and we're in business. Let's say that free hydrogen is contained within the fruit of a cactus-like plant growing in sulfur-rich soil. When the snail eats the plant, combined with the oxygen in the atmosphere, you get water. If the plant is left to decay, the hydrogen binds with sulfur in the skin to create hydrogen sulfide. $\endgroup$
    – JBH
    Sep 27, 2022 at 1:57
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    $\begingroup$ This is a real-world phenomenon, read up on metabolic water: en.wikipedia.org/wiki/Metabolic_water “Some organisms, especially xerocoles, animals living in the desert, rely exclusively on metabolic water. Migratory birds must rely exclusively on metabolic water production while making non-stop flights.” $\endgroup$
    – Ottie
    Sep 27, 2022 at 7:13

3 Answers 3


Hydrogen and Oxygen Love Hanging out

As described by others above, hydrogen and oxygen, if present in an atmosphere, tend to stick together and become water naturally, so you wouldn't need a creature to create water in an atmosphere that already has these two gases. However...

What if There is no Hydrogen in Your Atmosphere?

This premise allows for a wonderful (and, in your case, desired) allowance for a creature to have a diet consisting of something that has bonded to hydrogen, and through digestion, exudes hydrogen.

How would this work?

Assuming a food of some sort that has powerfully bonded hydrogen, your creature wouldn't be able to digest said hydrogen, and would "exhale" the hydrogen through its skin. The hydrogen would naturally bond with the oxygen around it, and thus produce water in a film (think a lot like sweat) around the creature whenever it digests its food.

How much water could this produce?

First, lets get some variables locked down.

  • A is the total weight of the miracle food the creature consumes.
  • B is the weight of elements that make up the compound that is the food.
  • C is the weight of specifically hydrogen * the number of hydrogen that are in the compound
  • D is .1111 (11.11%, the percentage of weight that hydrogen is in H2O)

In a mathematically ideal situation with 0 loss, your formula would look something along the lines of:


  • Cryptohalite: http://webmineral.com/data/Cryptohalite.shtml
  • Cryptohalite has a molecular weight of 178.15 gm (grams/mole). A mole is 6.02214076×10^23. In other words, that many particles has a weight of 178.15 grams.
  • Hydrogen makes up 4.53% of the molecular weight of Cryptohalite, therefore being 8.070195 grams.
  • Now, a chickfila sandwich weighs about 180 grams, and I can easily eat two of those in one sitting, so assuming your creature could digest Cryptohalite in similar weights fairly quickly, we can double that number to 16.14039 grams.
  • Assuming 16.14039 is only 11.11% of the total weight of water produced by the creature, the creature would produce 145.278(0378 repeating) grams of water!
  • With that measurement, you can now take the weight of the produced water (145.27803780378~) over the weight of the digested food (356.3), to get about a 40.77% return on digestion! With that you could tweak the amount of food the creature eats until it has enough to provide a human with enough water to live off of. Keep in mind that 1 liter of water is 1,000 grams.

Closing Thoughts

For this scenario, you would be best served creating a custom ecosystem of creatures that use each other to survive. Perhaps the creature eats fruit off of a tree, and that tree uses the water the creature provides to pump hydrogen into the fruit. Perhaps there are also outcrops of rock that have heavy hydrogen percentages that the creature can eat as well when it needs to. The world is your oyster, as long as you conform to chemistry I suppose.

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    $\begingroup$ i actually really liked this, explained it in a way my dumb brain could understand! thanks for the answer to my very (now as i can see it) simple problem $\endgroup$ Oct 17, 2022 at 22:45

If you have free hydrogen and oxygen in your atmosphere your problem won't be "can this creature burn them to make water?", but rather "how do I keep them separate long enough to allow life evolution?", because those two together are a constant safety hazard.

Luckily for you, oxidation of almost any organic substance produces as byproduct CO2 and H2O, so you don't have to venture that far into having an explosive atmosphere to have your creatures produce water.

For example oxidation of sugar follows this reaction:

$C_6H_{12}O_6 + 9O_2 \rightarrow 6CO_2 + 6H_2O$

where you can clearly see water coming out.

This gives you also a way of estimating how much water will they produce, once you can assume their daily metabolism and diet.

However mind that a 3 kg creature producing 2 kg of water as waste everyday feels a bit off, especially in a dry climate.

  • $\begingroup$ The reaction is even more advantageous when you start from fats (same as for energy production, there's just more to oxidise). Consider that hibernating animals can get away with never eating or drinking for months while they consume their fat stores. I don't remember enough of my lipid catabolism to come up with an actual number though. $\endgroup$
    – Ottie
    Sep 27, 2022 at 15:44

They should collect water, not produce it

If your planet has life that produces water as a biological biproduct, then over millions/billions of years of evolution, your planet will stop being a desert. A similar event that happened in Earth's history: The Great Oxidation Event. In this event, the introduction of photosynthesis dramatically changed our planet's atmosphere to go from <0.001% Oxygen to over 20% Oxygen. This event took a few hundred millions years, but only because there was so much unoxidized iron around to act as an oxygen sink. If not for this factor, it is estimated that the Great Oxidation Event could have happened in as little as 2 million years.

So if you want a life form that can be exploited for water, but without it being something that turns your planet into a water world, don't make it something that can "make" water, but something that can collect it in ways that your main character can not. If you want an organism that appears to make water out of nothing, you should consider condensation collection.

In Ethiopia, passive condensation towers like this can produce up to 80 liters of water per day by collecting it from the relatively dry desert air.

enter image description here

Since you're only looking for about 2 liters per day, a much smaller condensation system would be sufficient. I would suggest a creature kind of like a peacock that uses a large plumage as a condensation surface that funnels water down into some sort of bladder.

What if we are talking about a Carbon Planet?

Based on the OP's comments below, it looks like he is interested specifically in Carbon planets: worlds where Carbon is more plentiful than Oxygen. These world have a very different chemistry than our own and offer many unique hurdles to colonization beyond just water collection. Such a world, if formed in the Goldilocks zone would have an atmosphere full of methane, CO2, long chain hydrocarbons, and practically no O2. The rain and oceans would be made of tar and the crust would made largely of graphite and diamonds where ours is made mostly of silicates.

While water can be be produced from these sources, the consequences for producing water on a carbon planet are not good. Any water made by your slugs will be prone to react with all sorts of things in the environment making it unstable. The moment they secrete it, it would most notably react with the air to form carboxyl acid.

Rather than your slugs producing water as a waste product, they could produce it in leu of stomach acid to help with digestion. So, in a survival scenario, one could drink the stomach contents of a slug and it would basically be like drinking a soda. With the prevalence of hydrocarbons and CO2, they have all the building blocks they need to do this.

This said, a technologically advanced civilization would not need to murder millions of space slugs to provide for thier water needs. Using the Sabatier Reaction, a space faring civilization could much more easily use the methane and CO2 in the atmosphere to produce thier water in bulk. So, if your colonists resort to drinking slug guts as anything other than a bubbly treat, it's probably because something went wrong with thier Sabatier Reactor.

  • $\begingroup$ His planet could also be in the early stages of becoming livable, perhaps needing a few more million years to truly become viable for life, but you're very right in that condensation systems could be a very good way to explain his scenario. $\endgroup$ Sep 27, 2022 at 15:52
  • $\begingroup$ @shootbuildthink I thought about that, but it is unlikely to find complex life in a time that a planet is undergoing such a dramatic change in fundamental biology. A brand new type of water making extremophile bacteria I would believe, but complex life tends to have a lot more things that can go wrong; so, if your body suddenly starts mass producing a substance that was once very rare, it will probably kill you. $\endgroup$
    – Nosajimiki
    Sep 27, 2022 at 16:50
  • $\begingroup$ Very good point. While I was creating my answer, I was definitely thinking along the lines of a bacteria / single-celled organism of some sort that would be doing it, because realistically that's definitely the kind of organism that would perform such a function. $\endgroup$ Sep 27, 2022 at 18:24
  • $\begingroup$ in trms of the planets, it's supposed to be an extremely carbon-rich high-pressure planet, (for the production of natural diamonds near surface level, to be used as some form of mining outpost by an already space-faring race) although not what this is about, this would be a way to create an interesting way o getting water just to stir up the "boringness" of it and I would assume a carbon-dioxide rich atmosphere wouldn't be very friendly to water vapor (as i assume it reacts the same way as normal water as I'm not gifted at chemistry i haven't tried) $\endgroup$ Oct 17, 2022 at 22:42
  • $\begingroup$ as i am a very dumb person (relative to the rest of the people here) ignore anything that sounds like me stating fact, as its probably just an assumption fro me $\endgroup$ Oct 17, 2022 at 22:43

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